This invention relates to fuel cells, particularly to manifold-to-stack seals for fuel cells, and more particularly to a high creep capacity manifold sealing system for fuel cell stacks.
The fuel cell is a relatively new type of efficient electrical generator, which has been successfully used for space applications, for example, and which can have a favorable impact on the energy supply in the years to come.
A basic fuel cell comprises an anode electrode spaced apart from a cathode electrode with an electrolyte disposed therebetween in a compartment formed between the two electrodes; each electrode also includes a catalyst layer on the electrolyte side thereof. On the nonelectrolyte side of the anode electrode is a reactant gas chamber for carrying a fuel, and on the nonelectrolyte side of the cathode electrode is a reactant gas chamber for carrying an oxidant. The electrodes are constructed so that the gas diffuses therethrough and comes into contact with the electrolyte in the catalyst layer thereby causing an electrochemical reaction whereby ions travel from the cathode electrode through the electrolyte to the anode electrode. This flow of ions and the accompanying external electron flow is basically the electric current produced by the cell.
In a fuel cell power plant a number of fuel cells are connected electrically in series through plates separating adjacent cells, thereby forming a stack. These plates in combination with the electrodes adjacent thereto, generally define the reactant gas passages or chambers. The voltage across the stack is the sum of the voltages across the individual cells, which is a function of the current produced by each cell. The amount of reactant gas utilized by each cell is directly proportional to the amount of current produced in the electrochemical reaction.
Various types of fuel cells have been developed, as exemplified by U.S. Pat. No. 3,132,972 issued May 12, 1964; No. 3,282,736 issued Nov. 1, 1966; No. 3,364,071 issued Jan. 16, 1968; No. 3,979,224 issued Sept. 7, 1976; and No. 3,994,748 issued Nov. 30, 1976.
Substantial effort has been directed to fuel cell seals to prevent leakage of the gas from the cell and for sealing between the electrodes containing a corrosive liquid electrolyte which destroys the seals. These prior sealing efforts are exemplified by U.S. Pat. No. 3,323,950 issued June 6, 1967; No. 3,326,722 issued June 20, 1967; No. 3,365,334 issued Jan. 23, 1968; No. 3,389,017 issued June 18, 1968; No. 3,607,418 issued Sept. 21, 1971; and No. 3,743,544 issued July 3, 1973.
With the development of fuel cell stacks, it was necessary to provide the stack with fuel and oxidant manifolds for simultaneous supply to and exhaust of gases from the individual cells of the stack. Accordingly, it became necessary to provide manifold-to-stack seals to prevent leakage of the gases involved in the operation of the fuel cell stack. Also, during operation of the fuel cell stack, the stack undergoes compressive creep. Thus, since the stack is made up of a series of cells, the surface of the stack is rough, and with compressive creep of the stack, the manifold-to-stack seals were forced to slide against the rough surface of the stack as the stack becomes shorter because of cell creep. This relative motion destroys the seals.
It is thus seen that one of the most difficult sealing problems in the development of low-cost, commercial fuel cell stacks is to provide high-integrity seals, particularly for maintaining a low leak rate manifold seal as the stack undergoes compressive creep.